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Introduction to Epidemiology of Influenza A (HINI) Infection

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Title: Introduction to Epidemiology of Influenza A (HINI) Infection


1
Introduction to Epidemiology of Influenza A
(HINI) Infection
  • Dr. Tong Ka Io
  • Center for Disease Control Prevention
  • 4th May, 2009

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Outline
  • Situation update
  • Characteristics of the disease
  • Risk assessment
  • Preventive measures

4
Situation Update
5
Influenza A (H1N1) human cases (2009.05.04)
Confirmed Deaths
Mexico 590 25
US 226 1
Canada 85

20 other countries 985 26
6
Situation in Mexico
  • Jan to Mar 11 all samples reconfirmed to be
    negative
  • Mar 15/17 1st probable/confirmed case
  • Apr 12 reported to WHO an ILI outbreak in a
    small community (Veracruz)
  • Apr 17 Issued alert due to a case of atypical
    pneumonia (Oaxaca) and enhanced surveillance
  • Apr 23 Canada HPA helped to confirm swine flu
    infection and reported to WHO
  • Apr 27 School suspension in the whole country
  • May 3 Epidemic easing

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Asia Pacific region
  • Confirmed
  • New Zealand...6
  • Hong Kong1
  • Korea1
  • Suspected
  • Australia
  • Thailand
  • Japan

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Characteristics of Disease
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Virology
  • H1N1
  • Same virus found in Mexico and US
  • A new subtype not previously detected. A large
    part of the gene sequence is similar to that of
    the swine flu virus in US while a small part
    similar to that in Eurasia
  • Resistant to amantadine and rimantidine but
    sensitive to oseltamivir (Tamiflu) and zanamivir
    (Relenza)

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Epidemiology
Mexico US
Temporal distribution 03.15 03.28
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Number of confirmed (N 97) and probable (N
260) cases of swine-origin influenza A (H1N1)
virus (S-OIV) infection by date of illness
onset Mexico, March 15--April 26, 2009
25
Confirmed human cases of swine-origin influenza A
(H1N1) infection with known dates of illness
onset United States, March 28--April 27, 2009
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Epidemiology
Mexico US
Temporal distribution A double in the number of ILI cases over the country starting from the end of March All 32 states report suspected or probable cases Clusters of severe pneumonia cases and deaths in several administrative regions Cases first found in California and Texas that are adjacent to Mexico Cases are currently found in 30 states 63 in NY, 40 in Texas, 26 in California
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Epidemiology
Mexico US
Human distribution Confirmed cases are aged between 1-59. Fatal cases are mostly healthy people aged between 20 to 45 Fatal cases include healthcare workers and their families Confirmed cases are aged between 3-81, the median being 16. Non-healthcare workers, no contact history with pigs. The minority have travelled to Mexico but 85 are without travel history or contact history with confirmed cases.
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Number of patients and deaths from
laboratory-confirmed infection with swine-origin
influenza A (H1N1) virus (S-OIV) by age
group Mexico, April 1--27, 2009
32
Places of transmission
  • Families
  • Medical establishments
  • Schools

33
Clinical manifestation
  • Incubation undefined at present, estimated to be
    2-7 days by US. WHO adopts the longest incubation
    period of 14 days
  • Manifestation
  • US relatively mild self-limiting ILI. Vomiting
    and diarrhea are commonly seen
  • Mexico Mild cases are common, mostly with
    symptoms of fever, cough, shortness of breath,
    vomiting, diarrhea. Severe cases have rapidly
    developed severe pneumonia and severe acute
    respiratory disease with high fatality
  • Diagnosis RT-PCR on respiratory samples yields
    positive results for influenza A virus but unable
    to differentiate subtype

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Symptoms in an outbreak in a New York high school
  • Cough...98
  • Subjective fever...96
  • Fatigue..89
  • Headache..82
  • Sore throat82
  • Runny nose82
  • Chills..80
  • Myalgia..80
  • Nausea55
  • Abdominal pain50
  • Diarrhea48
  • Shortness of breath48
  • Joint pain46

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Mexico official sources
  • 25 among patients of ILI are suspected cases
  • Among which, 10 are hospitalized for observation
  • Among which, 1/3 are severe cases requiring an
    operation
  • Fatality rate approximately 1.2

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Risk Assessment
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WHO assessment
  • Event fulfils all 4 criteria for public health
    emergencies of international concern as defined
    in IHR (2005)
  • Serious public health impact unusual or
    unexpected international spread significant
    risk of international travel or trade
    restrictions
  • On April 25, on the advice of the Emergency
    Committee, WHO's Director-General announced that
    the situation constituted a public health
    emergency of international concern
  • Recommending all countries to heighten
    surveillance for unusual outbreaks of ILI and
    pneumonia

39
WHO assessment
  • On April 27, WHO's Director-General raised the
    level of influenza pandemic alert from phase 3 to
    phase 4, stating
  • Likelihood of a pandemic has increased but not
    inevitable
  • Virus is capable of human-to-human transmission
    and community-level outbreaks.
  • Given the widespread presence of the virus,
    containment of the outbreak is not feasible. The
    current focus should be on mitigation measures.

40
WHO assessment
  • On April 29, WHO's Director-General raised the
    level of influenza pandemic alert from phase 4 to
    5 , stating
  • The pandemic is imminent
  • All countries should immediately activate their
    pandemic preparedness plans
  • At this stage, effective and essential measures
    include heightened surveillance, early detection
    and treatment of cases, and infection control in
    all health facilities

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WHO phases of pandemic alert - Phase 4
  • Verified human-to-human transmission of an animal
    or human-animal influenza reassortant virus able
    to cause community-level outbreaks.
  • The ability to cause sustained disease outbreaks
    in a community marks a significant upwards shift
    in the risk for a pandemic.
  • Indicates a significant increase in risk of a
    pandemic but does not necessarily mean that a
    pandemic is a forgone conclusion.

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Phase 5
  • Human-to-human spread of the virus into at least
    two countries in one WHO region. While most
    countries will not be affected at this stage
  • Is a strong signal that a pandemic is imminent
    and that the time to finalize the organization,
    communication, and implementation of the planned
    mitigation measures is short.

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Phase 6 (pandemic phase)
  • Community level outbreaks in at least one other
    country in a different WHO region in addition to
    the criteria defined in Phase 5.
  • Indicate that a global pandemic is under way.

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Local assessment
  • More serious than SARS outbreak in Feb 2003
  • With both the characteristics of flu and SARS
  • Conforming to initial characteristics of a
    pandemic

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Influenza A (H1N1) vs. SARS
SARS 2003.02 Influenza A (H1N1) 2009.04
Development 3 mths 1 mth
No. of suspected cases and deaths 305 infected 5 died gt2000 infected gt100 died
Scope of transmission Limited to Guangdong Spread to 3 continents and at least 8 countries
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With characteristics of flu
  • Adapted for human transmission
  • Rapid transmission
  • Invisible transmission
  • Enlarged through outbreaks in schools

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Outbreak in a New York high school
  • Apr 23-24 222 sick students visited the school
    nursing office
  • Apr 26 7 out of 9 samples tested positive for
    influenza A (H1N1)
  • 44 preliminary confirmed cases
  • Onset date Apr 20-24
  • Aged between 14-21
  • 68 non-Hispanic white, 16 Hispanic, 5
    non-Hispanic black, 11 of other races
  • No travel history
  • ILI symptoms. Only 1 has to be hospitalized for a
    short period
  • Small number of students in the same school
    reported having travelled to Mexico

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Number of confirmed cases ( N 44) of
swine-origin influenza A (H1N1) virus infection
in a school, by date of illness onset New York
City, April 2009
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With characteristic of SARS
  • Causes severe acute respiratory tract infection
  • Super spreaders may exist
  • Enlarged through outbreaks in medical
    establishments

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Clusters of severe pneumonia cases
  • Cluster in San Luis Potosi involved 9 cases and 2
    persons died
  • Cluster in Mexicali involved 3 cases and 2
    persons died
  • Cluster in National Institute of Respiratory
    Diseases (INER) involved 6 cases and 2 persons
    died
  • Dead cases were a doctor and his daughter. The
    other daughter of the doctor was hospitalized for
    pneumonia
  • Rumour 2 interns died 6 days after being
    infected

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Conforming to initial characteristics of a
pandemic
  • Current situation in Mexico does not conform to
    expectations for a pandemic
  • Rapid international and inter-continental
    transmission
  • Initial stage (1st wave) is usually less severe
  • Severe cases and fatal cases are usually the
    young and prime aged

53
Questions to be answered
  • What is the real scope and transmission extent in
    Mexico?
  • How many reported pneumonia cases are caused by
    Influenza A (H1N1)?
  • Are these cases concentrated or widely dispersed?

54
Questions to be answered
  • Why cases in Mexico and US differ so much in the
    severity?
  • Weakened virus?
  • Super spreaders and outbreaks in medical
    settings?
  • Lifestyles/hygiene practices?
  • Level of medical services/vaccination?
  • Genetic difference?

55
Questions to be answered
  • Can the seasonal influenza vaccine offer partial
    protection?
  • According to US CDC, the seasonal influenza
    vaccine is unlikely to provide protection for
    Influenza A (H1N1)
  • Obviously, cases in Mexico are more severe than
    those in US. Fatal cases are mostly the young and
    prime aged.

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Prognosis impossible outcomes
  • A false alarm. Situation was being exaggerated
  • Outbreaks controlled or eliminated via public
    health measures

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Prognosis possible outcomes
  • Outbreaks stop by itself
  • Transmission continued without touching off a
    pandemic, eventually becoming part of the
    seasonal influenza
  • Resulting in a pandemic
  • Serious impact during the first wave
  • Serious impact only in the second wave

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2nd wave
1st wave
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Estimation for local region
  • Although the origin of outbreak is distant from
    Macao and there are no direct flights between the
    two places, early cases may be imported at any
    time
  • Once a pandemic has started, it will probably
    enter Macao within several weeks
  • Since 2005, the Influenza Pandemic Preparedness
    Plan and preparation in Macao is maintained at a
    satisfactory level. It is believed that when
    Macao is attacked by the pandemic, the impact on
    health, society and economics can be reduced to a
    minimum

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Preventive Measures
61
Vaccines
  • Vaccination is the best method of prevention
  • US CDC has begun to produce specific vaccines.
    However, mass production generally requires a
    period of 6 months

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1. Basic measures
  • Keep contact with WHO, China MOH, health
    departments of neighboring regions so as to
    obtain the latest information
  • Enhance risk communication and release timely
    information so as to inform all residents of the
    current situation and development, and adopt
    appropriate self-protection and personal hygiene
    measures
  • Meet with the media regularly to report and
    explain the outbreak development
  • CDC staff on duty and a 24-hr hotline in service
  • Health education and promotion via the community
    network
  • Health education and promotion by other
    government departments within their scope

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2. Deferment measures
  • Issue travel alert and travel warning according
    to situation so that residents can take
    appropriate measures before, during and after
    their trip
  • Strengthen temperature screening at all ports of
    entry, paying special attention to travellers
    from affected areas

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3. Early detection and isolation
  • Heighten surveillance for ILI and outbreaks,
    virology of influenza, pneumonia of unknown
    causes
  • Maintain close relationship and collaboration
    with WHO influenza laboratory network to increase
    the ability of virus testing
  • Issue guidelines to public, private medical
    settings and healthcare workers so as to promptly
    detect and refer suspected cases
  • Examine and repair isolation facilities and
    equipment so as to isolate suspected and
    confirmed cases when necessary

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4. Measures to prevent outbreaks in high-risk
institutions
  • The Health Bureau coordinates all medical
    institutions to maintain good infection control
  • With the help of DSEJ, coordinates all schools to
    perform preventive measures such as morning
    inspection, temperature measurement, school
    suspension for the sick, outbreak notification
    better and revise contingency plans so as to
    suspend school when necessary
  • With the help of IAS, coordinates all nurseries
    to perform measures such as morning inspection,
    temperature measurement, school suspension for
    the sick coordinates all social facilities for
    outbreak notification, better and revise
    contingency plans so as to suspend social
    services when necessary

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5. Measures to respond to pandemic
  • Health Bureau perfects and revises the Influenza
    Pandemic Preparedness Plan and substantial
    preparation so as to rapidly adjust functions,
    allocate resources, raise capacity and rescue
    patients in times of a pandemic
  • All relevant departments perfect and revise
    preparedness plans and substantial preparation so
    as to maintain basic social functions and
    services in times of a pandemic

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6. Restorative measures
  • All relevant departments perfect and revise
    post-pandemic restorative plans and preparation
    for social, economic, psychological aspects so as
    to achieve fast recovery of the community after
    the pandemic.

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